Consider the following reaction: CH3OH(g) ==== CO(g) + 2 H2(g) H = +90.7 kJ a) I

Question

Consider the following reaction: CH3OH(g) ==== CO(g) + 2 H2(g) H = +90.7 kJ

a) Is heat released or absorbed in the course of this reaction?

b) Calculate the amount of heat transferred when 45.0 g of CH3OH(g) is decomposed by this reaction at constant pressure.?

c)For a given sample of CH3OH, the enthalpy change upon reaction is 25.8 kJ. How many grams of hydrogen gas are produced? What is the value of H for the reverse of the previous reaction?

d) How many kilojoules of heat are released when 50.9 g of CO(g) reacts completely with H2(g) to form CH3OH(g) at constant pressure?

Explanation / Answer

Ans.    CH3OH(g) ---> CO(g) + 2H2                      ; dH= +90.7kJ

#a. dH = + 90.7 kJ. The plus (+) sign indicates that heat is being absorbed in course of reaction.

#b. Stoichiometry: 1 mol CH3OH decomposes into 1 mol Co and 2 mol H2, with absorption of 90.7 kJ energy. Since the reaction represents decomposition of 1 mol methanol, the enthalpy change is for 1 mol. That is, decomposition of 1 mol methanol requires 90.7 kJ energy, or the molar enthalpy of reaction = +90.7 kJ/mol.

Now,

            Moles of CH3OH in 45.0 g sample = mass/ Molar mass

                                                            = 45.0 g/ (32.04216 g/mol)

                                                            = 1.40 mol

Amount of heat absorbed = Moles of CH3OH decomposed x Molar enthalpy

                                                = 1.40 mol x (90.7 kJ/mol)

                                                = 126.98 kJ

#c. dH for reverse of previous reaction (#2) = - dH for #2 reaction = - 126.98 kJ. The negative sign indicates that heat is being released when reaction is reversed.

Moles of CH3OH decomposed = Heat absorbed / molar enthalpy

                                    = 25.8 kJ / (90.7 kJ/mol)

                                    = 0.28 mol

See the stoichiometry, 1 mol CH3OH produces 2 moles H2.

So,

            Moles of h2 produced = 2 x moles of CH3Oh decomposed

                                                = 2 x 0.28 mol

                                                = 0.56 mol   

#d. CO(g) + 2 H2(g) --> CH3OH                ; dH = - 90.7 kJ/mol             - Reversed

Stoichiometry: 1 mol CO reacts with 2 mol H2 to form 1 mol CH3OH, with release of 90.7 kJ energy. 1 mol CO releases 90.7 kJ energy when converted into methanol.

Moles of CO in 50.9 g sample = Mass / molar mass

                                    = 50.9 g / (58.9332 g/mol)

                                    = 0.864 mol

Amount of heat released = moles of CO x dH of reaction

                                    = 0.864 mol x (90.7 kJ/mol)

                                    = 78.3648 kJ

Related Questions

Navigate

• Browse (All)
• Browse C
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.